| With the increasing power load in China and the gradual improvement of UHV power grid,bushings are widely used as common outlet components of transformers,and resin-impregnated paper bushings with epoxy resin impregnated wrinkled paper as the main insulation core have attracted much attention because of their remarkable performance.However,due to harsh electrothermal conditions and process level problems,accidents such as radial breakdown inside the core and axial flashover on the surface have occurred,which have a huge impact on the reliability of the power grid.At present,due to the variety of defects,the development process and characteristic changes are not clear,so the research on the development process and characteristics of typical defects of resin-impregnated paper bushing is carried out to provide experimental basis and reference for solving the problem of the development of actual bushing defects.Aiming at the problem of unclear evolution of dielectric characteristics of resin-impregnated paper materials under the action of electrothermal action,a long-term experimental development platform for electrothermal testing with simultaneous electrical and thermal application of resin-impregnated paper materials was constructed,and the development and change law of volume resistivity and dielectric spectrum of resin-impregnated paper materials under the long-term action of electrical stress,thermal stress and electrothermal stress was studied.The results show that under the 16-day test cycle,the volume resistivity of resin-impregnated paper under thermal and electrothermal stress shows a downward trend with the increase of test time,and the dielectric spectrum shows an upward trend.The volume resistivity of resin-impregnated paper under the action of heat,electric heating and electric stress decreased by 62.0%,75.2%and 11.8%compared with the initial state,the increase of power frequency dielectric constant was 5.61%,6.23%and 0.51%,and the increase of power frequency dielectric loss was 104.96%,123.97%and 14.05%,respectively.Aiming at the problem of discharge development and unclear characteristics of typical defects of resin-impregnated paper bushing,this paper designs the solid model of four typical defects of bushing from a practical point of view:poor impregnation bubble defect,plate burr defect,plate breakage defect and core edge defect,and uses electric field finite element simulation to verify the equivalence.A typical defect discharge development platform with partial discharge online detection was built,the development process of partial discharge was studied by pulse current test method and step-up method,the discharge spectra of different discharge stages were constructed,the characteristic parameters of discharge repetition rate,total discharge amount,maximum discharge amount and average discharge amount could be extracted to characterize the discharge development,and the overall stage of discharge development of four typical defects was divided by using the change trend of discharge spectrum and discharge characteristic parameter to divide the overall stage of discharge development of four typical defects.It provides a reference for assessing the severity of partial discharge.The results show that the overall stage is divided into discharge initiation stage,discharge development stage and discharge danger stage,and the main characteristics are:discharge initiation stage,less discharge amount,sparse and intermittent discharge,low discharge repetition rate,and narrow discharge distribution along the phase.In the stage of discharge development,the discharge amount and discharge repetition rate increased significantly,the discharge distribution along the phase became wider,and the discharge point increased by 330°～360°.In the discharge danger stage,the discharge amount reaches the maximum value of the entire discharge process,the discharge is the widest distribution along the phase,and the partial discharge intensity reaches the maximum value,which can provide a reference for the assessment of the severity of partial discharge of the bushing. |
